$ { \left[\begin{array}{r}{1} \\ {-1} \\ {-2}\end{array}\right]+\left[\begin{array}{r}{-2} \\ {0} \\ {0}\end{array}\right] = {?} } $
To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{r}{1}+{-2} \\ {-1}+{0} \\ {-2}+{0}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{-1} \\ {-1} \\ {-2}\end{array}\right]}$